Robots, like animals, are typically designed for five fundamental functions, namely, sensing, signaling, motion, intelligence and a source of energy. Industrial robots, that perform repetitive or explicitly defined functions in a static, mapped environment (e.g., robot arms) require: sensors to determine their position; lights to signal activity; electronic motors to move their limbs or grippers; a computer to direct the motion and run feedback loops and a tethered, electrical supply of power.
In contrast, service robots must be capable of interacting safely with humans in a dynamic, unmapped environment. These types of robots typically require sensors that are capable of detecting obstacles; a computer running sophisticated software to direct their motion and environmental interactions and a source for power. Nevertheless, these robots also suffer from drawbacks. The requirements of being able to dynamically sense, learn, and interact safely with an unmapped environment causes these robots to be slow and the power requirements for computers, motors and batteries results in excessive cost for fabrication of these robots.
Robotic systems used for industrial automation or service robots are manufactured from precisely machined hard parts with electric motors that require sensors to enable accurate control of their motion. Suitable examples of these sensors are cameras, accelerometers, and position encoders that provide the input to feedback loops. The algorithms used in this type of active control systems work well in static, well defined, and pre-mapped environments, but often have great difficulty adapting to the kinds of unstructured and complex terrains found in nature.
In contrast, insects such as spiders and cockroaches possess compliant structures or limbs that enable passive adaptability to unpredictable and dynamic environments, without requiring a complex control system. The control system in these animals is referred to as “embodied intelligence” and extends beyond the brain and into the physical design and construction of the body and limbs of the insect, which is analogous to the electronic system and actuators of the robot, respectively.
The design principle of “embodied intelligence,” places some control and mechanical compliance directly into the limbs of the robots. Using this principle a new trend has emerged in the robotics industry and are seen in robots such as RHex (Kod Lab, UPenn), or DASH (Biomimetic Millisystems Lab, Berkley). Newer industrial robots such as Baxter (Rethink Robotics) rely on Series Elastic Actuators that couple electric motors to the limbs using an elastic linkage. This design provides the robotic arms with lower reflected mechanical impedance and increases safety in the human-robot interaction.
In an attempt to mimic the functions of gripping, camouflage, and locomotion found in animals such as the octopus or squid, soft elastomers have recently been used to develop a new type of nature-inspired robot, called “soft robots.” These “soft robots” are typically designed using silicone elastomers that are less dense and more flexible than the metals used in conventional “hard robots.” Due to their inherent mechanical compliance and the fact that they are softer than humans, these robots are capable of interacting safely in a dynamic, unmapped environment without inflicting any harm. However, a size limitation is imposed due to the low stiffness-to-density-ratio (κ:ρ) of the material. Silicone elastomers are too heavy to be used as support material in medium to large-scale robots that need to move quickly and efficiently.
In nature, the above problem is addressed by combining materials with complementary properties. A low-density material such as bone is used to form the load bearing skeletal support, whereas a higher-density material like muscle is used to actuate motion. This facilitates support of a larger amount of weight while at the same time allowing for quick and efficient operation with a greater range of motion. Further, nature uses tendons in the joints to store energy in the extension phase of the gait which is released on contraction. This increase the animal's output power and mechanical efficiency.
In an effort to recreate this power and efficiency, new robotic joints that are modular in nature and combine an elastomeric actuation device with a structural support are desired. Currently, robots of this sort that are light-weight, low-cost, and do not require elaborate assembly and fabrication are not available.